Electrodeposition of copper from an acid bath



United States Patent ELECTRODEPOSITION OF COPPER FROM AN ACID BATH Henry Brown, Huntington Woods, and Richard A; Fellows, Grosse Pointe, Mich., assignors to The Udylite Research Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application May 20, 1957 Serial No. 660,426

8 Claims. (Cl. 204-52) The present invention relates to the electrodeposition of copper from an aqueous acidic bath and more par-' ticularly concerns the provision of selected addition agents E for such baths for the purposes hereinafter stated.

The primary object of this invention is to provide a copper deposit which is fine-grained and which has a' high degree of luster and brightness as obtained directly from an aqueous acidic electroplating bath.

A further object of this invention is to provide an aqueous acidic copper electroplating bath which has a high rate of brightening and good leveling power to cover polishing lines and surface imperfections.

A still further object of this invention is the provision of an aqueous, acidic, copper, electroplating bath which is capable of producing highly lustrous deposits over a wide range of concentration of the brightener additives of this invention. I

Another important object of this invention is to provide brightener additives for aqueous, acidic,.copper, electroplating baths which may be employed over a relatively wide range of concentrationvand in concentrations in excess of the optimum concentration without obtaining undesirable striations in the resultant plate.

In accordance with this invention it has been found that an unexpectedly high rate of brightening and increased leveling of polishing lines and surface imperfections may be achieved by the conjoint use of a brightener additive of Table I together with a compound represented by Formula A.

r The thiohydantoin brightener additives of this invention and the optimum concentration of each in acidic, aqueous, copper, electroplating baths are set forth in Table I, and it is to be understood that mixtures thereof may be used in quantities equivalent to that employed for a single compound.

TABLE I Ooncen- Optimum tration, 001.10., grams/liter grams/liter 1. Thiohydantoin 0.002-003 0. 005-0. 015 2. 1-acetyl2-thlohydantoin 0002-003 0. 005-0. 015 3. l-propionyl 2-thiohydantoin 0. 002-0. 03 0. 005-0. 015 4. I-trlfiuoro acetyl 2-thiohydantoin 0. 002-0. 03 0. 005-0. 015

v Patented Apr. 14, 1959 The use of these materials in combination additionally permits the use of a wide range of, concentration of the compound of Table I within which an extremely bright copper plate may be obtained. Moreover'the presence of one or more of the compoundsrepresented by Formula A in combination with one or more of the compounds of Table I decreases the rate of depletion by electrochemical deposition of the compound of Table I and therefore increases its life and thus reduces the over-all cost of operation of the bath. Broadly the organic compounds which are useful in combination with the compounds of Table I, are represented by Formula A.

Formula A v wherein R and R are radicals selected from the group i consisting of hydrogen, methyl and ethyl radicals, X is an anion selectedfrom the group consisting of chloride,

and alkoxy substituent groups. The anion X is relatively unimportant and in addition to the anions above given may be any one of a wide variety of other anions includ ing organic anions such as formate, acetate, propionate, etc. It will be appreciated that the compounds represented by Formula A when present in an acid copper bath are highly ionized substances and the anion X is in ionic admixture with the other anions of the bath such as the sulfate anion, the nitrate anion, etc;

The thiohydantoin compounds of Table I function in an apparently unique manner -in combination with the compounds represented by Formula A, since it has been found that certain other ring type sulfur compounds do not enhance the brightening which is obtained from the use of compounds represented by Formula A alone. For example, this has been found to be true of thioparabanic acid and thiobarbituric acid, i.e., no appreciable brightening is obtained when thioparabanic or thiobarbituric is used in combination with the compounds of Formula A relative to that which is caused by the sole presence of a with this invention and in the ranges of proportions -indi,--

cated are given in Table II.

TABLE 11 Cone. gJl. Optimum 00110., g./l.

1. CH;- CH: .0015-.05 ADS-.015 (mmu-N- N -Gremlin ClN a, Diethyl sstranlne azo dimethyl aniline-J anus Green B cm .oo1s-.05 .oo3-.o1s

Diethyl safra'nine m phenol-Janus Black 3. CH CH: DE 0015-. 05 .003-.016

KIN N:

Cl--'-N Satranine azo naphthol-Ianus Blue 4. Janus Gray (Color Index 137, Society of Dyers & Colourists,

by F. M. Rowe, 1924) 0015-.05 003-. 015 5. Dimethyl safranine azo dimethyl aniline 0015-. 05 003-.015 6. Phenosafrunine 002-.03 003-. 010 7. Fuchsia 002-.03 003-.010 8. Amethyst Violet- 002-.03 003-.0

Mixtures of the dyes shown in Table II may also be employed with beneficial effects. Where mixtures are employed, however, the total concentration of the mixed dye in the aqueous acidic bath preferably approximates the concentration of any component of the mixture as is indicated in Table II. For general purposes, concentrations of dyes of Table II falling within the range of .005 to .03 gram/liter represent preferred quantities.

The composition of the acidic copper bath may vary over rather wide limits, although for the best grain refinement, rate of brightening and for the widest bright plating range, the following composition, designated Formula B, is recommended for use:

Formula B Concentration, Preferred grams/liter Concentration,

gramsfliter cuso -'H 0 150-250 170-200 H73 rill-"Uh" 10-30 15 Cathode agitation and preferably uniform air agitation is desirable. Cathode current densities of 10-100 amps/sq. ft. (approximately 1-10 amps./sq. dm.) may be satisfactorily employed with the particular current density depending primarily upon the degree of agitation of the cathode film and the shape of the article to be plated. For general purposes, an average cathode current density of 30-50 amps/sq. ft. may be used.

As a substitute for the sulfuric acid of Formula B, nitric acid or phosphoric acid may be used in approximately equivalent proportions. Additionally, Formula B may include other ions for the purpose of increasing the conductivity of the solution such as sodium, potassium or ammonium ions. These ions are, usually present in only minor concentrations. Furthermore, the copper sulfate of Formula B may be replaced by copper nitrate in approximately equivalent proportions, and when acidified with small amounts of phosphoric acid, nitric acid or sulfuric acid, the beneficial eflFect of reducing the grain size and increasing the luster of the deposit by additions of small concentrations of compounds of the type shown in Table I is also evident. The degree, however, of grain size, reduction and increase in luster is somewhat less extensive than is produced from the use of acidic baths made up primarily of copper sulfate. In general, the copper sulfate or copper nitrate concentration in the bath may satisfactorily vary from as low as about 100 grams/ liter up to saturation. Concentrations of acid above the equivalent in acidity of about -100 grams/liter of sul'v '5 furic acid decrease the brightening efiect of the addition agents represented by Formula A and are therefore to be avoided.

Small concentrations of wetting agents may be advantageously present in the baths of this invention. For example, the surface-active compounds, sodium decyl sulfate and the sodium salt of sulfated monoethylene glycol ether of decyl alcohol when present in small concentrations'of about .01 to .06 gram/liter are efiective in de creasing pitting and striation formation in the deposit due to the presence of harmful organic compounds or excessive concentrations of brighteners. These wetting agents normally cause excessive frothing with air agitation, but in the presence of the addition agents of Table II, the frothing is minimized.

-.The following typical plating baths are given by way of example to illustrate the invention in greater detail.

, EXAMPLE I CuSO .5H O grams/liter 200 H 80 do 15 lcetyl, Z-thiohydantoin do 0.015 Phenosafranine do 0.005 Temperature F 70-95 Cathode current density amps./sq. ft 30-40 Air. agitation. I 1 f EXAMPLE II CuSO .5H O grams/liter 200 H 80 do 15 l-propionyl, 2-thiohydantoin do 0.015 Janus Green B do 0.010 Sodium N-decyl sulfate do .01-.03 Temperature F 70-95 Cathode current density ampsJsq. ft 30-40 Air agitation.

EXAMPLE III CuSO .5H O "grams/liter-.. 200 NI-LNO do 20-30 H 80 dn 15 Janus Green B do .015 l-acetyl, 2-thiohydantoin do 0.01 Temperature F 70-95 Cathode current density amps./sq. it... 30-50 Air agitation.

EXAMPLE IV Cu(NO grams/liter 200 do Janus Black do .010 l-acetyl 2-thiohydantoin do 0.01 Sodium salt of sulfated monoethylene glycol ether of decyl alcohol do .01-.03 Temperature F 70-95 Cathode current density amps./sq. ft 30-50 Air agitation.

EXAMPLE V CuSO .5H O "grams/liter..- 200 H 50 do Janus Green B do .006-.015 l-trifluoro acetyl 2-triohydantoin do 0.01 Sodium salt of sulfated monoethylene glycol ether of decyl alcohol do .01-.03 Temperature F 70-95 Cathode current density amps./sq. ft 30-40 Air agitation.

EXAMPLE VI CuSO .5H O "grams/liter" 200 H 80 do 15 Janus Green B d .05 Thiohydantoin do 0.01 Temperature F 70-95 Cathode current density amps./sq. ft 30-40 Air agitation.

EXAMPLE VII CuS0 .5H O grams/liter 200 H do 15 l-trifluoro acetyl Z-thiohydantoin ...do 0.015 Amethyst Violet do 0.005 Temperature F 70-95 Cathode current density ampsjsq. ft 30-40 Air agitation.

EXAMPLE VIII CuSO .5H O grams/liter 200 H3504 an Thiohydantoin do 0.015 Fuchsia n do 0.005 Temperature F 70-90 Cathode current density amps./sq. ft 30-40 Sodium decyl sulfate gram/liter .03 Air agitation.

This application is a continuation-in-part of our copending application, Serial No. 384,758, filed October 7, 1953, now abandoned.

What is claimed is:

1. A bath for the electrodeposition of copper comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, about 0.002 gram/liter to about 0.03 gram/liter of a compound selected from the group consisting of thiohydantoin, 1-acetyl-2-thiohydantoin, l-propionyl-Z-thiohydantoin and l-trifluoro acetyl 2-thiohydantoin, and 0.0015 to 0.05 gram/liter of a compound having the structure:

wherein R and R are selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, Y is a radical selected from the group consisting of H, NH N(CH and -N=NZ, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxy and alkoxy substituent groups.

2. A bath for the electrodeposition of copper comprising an aqueous acidic solution of a material selected from the group consisting of copper sulfate and copper nitrate, about 0.002 to about 0.03 gram/liter of a compound selected from the group consisting of thiohydantoin, l-acetyl 2-thiohydantoin, l-propionyl 2-thiohydantoin and l-trifiuoro acetyl 2-thiohydantoin and about 00015 to about 0.05 gram/liter of at least one compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl safranine azo dimethyl aniline.

3. A process for electrodepositing copper which comprises the step of electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, about 0.002 gram/liter to about 0.03 gram/liter of a compound selected from the group consisting of thiohydantoin, l-acetyl Z-thiohydantoin, l-propionyl 2-thiohydantoin and gram/liter of acompound having the structure:

wherein R and R are selected from the group consisting of hydrogen, methyl and ethyl radicals, X is an anion selected from the group consisting of chloride, bromide, iodide, fluoride, sulfate, bisulfate and nitrate, Y is a radical selected from the group consisting of H, -N(CH and -N=NZ, and Z is an aromatic radical selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl radicals substituted with amino, alkyl substituted amino, hydroxyand alkoxy substituent groups.

4. A process for electrodepositing. copper which comprises the step of electrolyzing an aqueous acidic copper solution containing a metal salt selected from the group consisting of copper sulfate and copper nitrate, about 25 0.002 to about 0.03 gram/liter of a compound selected from the group consisting of thiohydantoin, l-acetyl 8 2-thiohydantoin, 1-pro ionyt 2-thiohyda1itoin and l-trifluoro acetyl Z-thiohydantdiir and 0.001 5 to 0.05 g'fair'is'i/ liter of at least one compound selected from the group consisting of Janus Green, Janus Blue, Janus Black, Janus Gray and dimethyl safranin'e az'o dimethyl aniline.

5. A bath in accordance with claim 2 wherein the se lected materials are l-propionyl Z-thiohydantoin and Janus Green.

6. A process in accordance with claim 4 wherein the selected materials are l-propionyl 2-thiohydantoin and Janus green.

7. A bath in accordance with claim I wherein the se lec'ted materials are l-propionyl' Z-thiohydantOin and Fuchsia.

8. A process in accordance with claim 3 wherein the selected materials are" l-propionyl 2-thioliydantoin and Fuchsia.

References Cited in the file of this patent UNITED STATES PATENTS 2,707,166 Brown et a1. Apr. 26,- 1 935 2,738,318 Fellows et a1 Man-13,1956- FOREIGN PATENTS 461,186 Canada Nov. 22, 1949 

1. A BATH FOR THE ELECTRODEPOSITION OF COPPER COMPRISING AN AQUEOUS ACIDIC SOLUTION OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF COPPER SULFATE AND COPPER NITRATE, ABOUT 0.002 GRAM/LITER TO ABOUT 0.03 GRAM/LITER OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF THIOHYDANTOIN, 1-ACETYL-2-THIOHYDANTOIN, 1-PROPIONYL-2-THIOHYDANTOIN AND 1-TRIFLUORO ACETYL 2-THIOHYDANTOIN, AND 0.0015 TO 0.05 GRAM/LITER OF A COMPOUND HAVING GTHE STRUCTURE: WHEREIN R1 AND R2 ARE SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, METHYL AND ETHYL RADICALS, X IS AN ANION SELECTED FORM THE GROUP CONSISTING OF CHLORIDE, BROMIDE, IODIDE, FLUORIDE, SULFATE, BISULFATE AND NITRATE, Y IS A RADICL SELECTED FROM THE GROUP CONSISTING OF H, -NH2, -N(CH3)2 AND -N$N-Z, AND Z IS AN AROMATIC RADICAL SELECTED FORM THE GROUP CONSISTING OF PHENYL, NAPHTHYL, AND PHENYL AND NAPHTHYL RADICALS SUBSTITIUTED WITH AMINO, ALKYL SUBSTITUTED AMINO, HYDROXY AND ALKOXY SUBSTITUENT GROUPS. 